<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        body {
            margin: 0;
            padding: 0;
            background: grey;
        }
    ul{
        width: 400px;
        height: 100px;
        border: 1px solid red;
        list-style: none;
        margin-top: 100px;
        margin-left: 100px;
    }
    li{
background-color: yellow;
height: 30px;
    }
        /*提示框容器*/
        .tip {
            position: relative;
            margin-left: 20px;
            /* margin-top: 20px; */
            width: 200px;
            background: #fff;
            padding: 10px;
            bottom: 75px;
            /*设置圆角*/
            /* -webkit-border-radius: 5px;
            -moz-border-radius: 5px; */
            border-radius: 5px;
            display: none;
        }
        /*提示框-下三角*/
        .tip-trangle-bottom {
            position: absolute;
            bottom: -10px;
            left: 20px;
            width: 0;
            height: 0;
            border-left: 15px solid transparent;
            border-right: 15px solid transparent;
            border-top: 15px solid #fff;
        }
    </style>
</head>
<body> 
    <ul>
        <li>我是li标签
    <div class="tip">  
        <div class="tip-trangle-bottom"></div>
        我是提示框内容可以自定义  
    </div>
</li>
</ul>
    <script src="./triangle .js"></script>
</body>
</html>